Attoliter Mie Void Sensing

Abstract

Traditional nanophotonic sensing schemes utilize evanescent fields in dielectric or metallic nanoparticles, which confine far-field radiation in dispersive and lossy media. Apart from the lack of a well-defined sensing volume, these structures suffer from the generally limited access to the modal field, which is one key aspect for sensing performance. Recently, a novel strategy for dielectric nanophotonics has been demonstrated, namely, the resonant confinement of light in air. So-called Mie voids created in high-index dielectric host materials support localized resonant modes with exceptional properties. In particular, these structures benefit from the full access to the modal field confined strongly inside the void. We utilize these Mie voids for refractive index sensing in single voids with volumes down to 100 attoliters and sensitivities on the order of 400 nm per refractive index unit. Taking the noise of our measurements into account, we demonstrate detection of refractive index changes as small as 1 × 10^–3 in a defined volume of just 390 attoliters. The combination of our Mie void sensor platform with appropriate surface functionalization will even enable specificity to biological or other analytes of smallest volumes while maintaining said sensitivity.